The present disclosure relates generally to downhole well-logging tools and, more particularly, to downhole well-logging tools that employ a segmented radiation detector.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
A variety of downhole tools may be used to determine the properties of a subterranean formation or borehole fluid. Many such downhole tools may emit radiation, such as neutrons, x-rays, and/or gamma-rays into the materials that surround the downhole tool (e.g., the borehole fluid and/or the surrounding formation) to determine certain properties of the materials. To provide one example, X-rays or gamma-rays may interact with the materials of the borehole fluid and/or formation through Rayleigh and/or Compton scattering. The degree to which these interactions occur may affect the amount and energy of the radiation that returns to the downhole tool. Thus, by measuring the returning radiation, certain properties of the surrounding materials may be estimated.
Conventionally, these downhole tools may detect the returning radiation using one or more radiation detectors positioned to detect specific angles outside of the downhole tool. That is, each detector may detect radiation that returns to the downhole tool from only one azimuthal angle. Each detector may detect radiation from one side of the downhole tool, which may present an incomplete understanding of the materials on all sides of the downhole tool. Some techniques have been developed that involve rotating a downhole tool and/or the detectors of the downhole tool to detect radiation from other azimuthal angles. However, such mechanical rotation introduces additional complexity and potential points of failure.
Additionally, downhole tools used to determine the properties of a subterranean formation or borehole fluid may employ radioisotopic gamma-ray sources, but the use of such radioisotopic sources may have a variety of disadvantages. Specifically, such downhole tools may emit radiation using a first radioisotopic gamma-ray source, such as 137Cs, while using other radioisotopic gamma-ray sources of relatively lower strength as reference sources to emit a known amount of radiation directly at the radiation detectors. Because the sensitivity of the radiation detectors may vary and also may depend on environmental factors, which may change greatly as the downhole tool travels through the formation, the gain of the radiation detectors may be stabilized based on the radiation emitted by the reference sources. However, as mentioned above, the use of such radioisotopic sources may have several drawbacks. For example, radioisotopic sources in downhole tools may require special handling when the radioisotopic sources are inserted into or removed from the downhole tool. Additionally, these radioisotopic sources may require additional shielding during transportation and storage, as well as additional security during such transportation and storage. Indeed, in many countries, even very-low-strength radiation sources (e.g., 10−6 Ci) may be considered radioisotopic sources subject to burdensome regulations.